Solder alloys are used, for example, to connect an electrode of an electronic device with another portion or to join an IC device to a shielding case and further a heat sink. Such solder alloys metallically join an electrode to a circuit board or an IC device to a shielding case or the like by making use of the wettability on metal constituting the electrode or the like.
Cu plating is often used on a surface of an electrode or the like to be joined by soldering. However, Ni plating is also often used. Therefore, cases where not only a Cu-plated surface but also an Ni-plated surface is soldered are often seen. Accordingly, solder alloys having excellent solderability on both Ni and Cu are required.
In general, soldering on an Ni-plated surface is difficult and hence a thin layer of Au or other metal has conventionally been formed by plating on the Ni-plated surface before soldering thereon.
As for the soldering on an Ni-plated surface, a Pb—Sn based solder alloy (Patent Literature 1: JP 60-166192 A), a Bi—Ag based solder alloy (Patent Literature 2: JP 2005-503926 A) and an Sn—Zn based solder alloy (Patent Literature 3: JP 2005-52869 A) have conventionally been proposed for use in die bonding.